The field of the invention is vision testing. In particular, the invention concerns screening for peripheral scotomas.
Evaluation of a patient""s vision typically relies upon a patient""s ability to perceive normal visual stimulus. This limits diagnosis because patients experiencing peripheral visual field damage often remain visually asymptomatic. Patients often fail to notice any disturbance of the visual field until damage occurs close to the fovea. One of the most challenging problems in ophthalmology is the development of effective retinal screening tests for peripheral retinal disease.
Repression of pathologic blind or dark spots in a person""s visual field, i.e., scotomas, is related to the Troxler phenomenon. In the Troxler phenomenon, a fixed spot of light above threshold presented to the peripheral visual field will disappear from view. This phenomenon applies primarily outside 12 degrees from fixation. This is likely due to neural mechanisms in the brain. The phenomenon is valuable to human vision in several respects. As an example, the Troxler phenomenon allows eye structures in a constant position in the visual field, e.g., blood vessels, to be repressed. It also permits most cortical function to remain focused on a centrally placed object of regard, except when peripheral items are moving or changing in luminosity. However, scotomas due to retinal injury or other pathology are also repressed by the Troxler phenomenon, and therefore are not perceived by patients being tested, especially if they are far from the fovea.
There are a large number of diseases which affect the peripheral retina which current screening methods are unable to detect with a high sensitivity (i.e., ocular melanoma, diabetic retinopathy, CMV retinitis, branch retinal vein occlusion). Early stages of glaucoma can exhibit such a repressed loss of peripheral visual field sensitivity producing wedge-like defects in the peripheral visual field. Left untreated, glaucoma often progresses to affect the central ten degrees of vision whereby patients then often become symptomatic. There are also diseases of the optic nerve (e.g., optic neuritis) and primary visual cortex (e.g., AVM producing homonymous hemianopias) which produce scotomas that are often repressed. Early detection of all diseases first affecting peripheral vision is accordingly essential for the prevention of severe vision loss.
The standard diagnostic tool to diagnose peripheral scotomas has been threshold perimetry. Entoptic, or snow-field perimetry, has been used to detect CMV retinitis, ocular melanoma, age-related macular degeneration, nonproliferative diabetic retinopathy, branch retinal occlusion, and other diseases with sensitivities and specificities over 95%. This technique uses a computer monitor filled with random particle motion. When the monitor is viewed by a person with normal vision, the screen appears as xe2x80x9cvisual noisexe2x80x9d. Subjects with peripheral retinal lesions are able to outline their scotomas. Those areas corresponding to the damaged retina appeared to have no random motion, and are described by patients as xe2x80x9cgrayxe2x80x9d or xe2x80x9cmotionlessxe2x80x9d in appearance. The areas where patients perceive a lack of random particle motion correspond to retinal lesions.
Increasing the field of vision which may be tested using snow field perimetry requires larger computer screens and moving the patient as close as possible to the screen. Large screens require a large amount of space to use and store the equipment. Moving patients closer to the screen produces a distortion of the stimulus as people get close to the large screen (but outside the accommodative limit) while attempting to view the image in the peripheral retina. Patients, particularly geriatric populations who typically suffer from many of these diseases, are unable to accommodate well and cannot be placed close to screen to increase the stimulus size on the visual field. Furthermore, the screens suffer from poor contrast and a lack of lighting control. In addition, testing suffers from refractive and accommodative error correction.
Thus, there is a need for an improved peripheral scotoma screening diagnostic technique, and an improved device to aid such screening. The invention is directed to that need.
The present invention meets such a need. The invention utilizes a virtual reality display to present a random noise stimulus to a patient. Using an input device, a patient indicates the location of visual field disturbances in the random noise display. In a preferred embodiment, a scanning retinal laser projects the random noise stimulus directly onto a patient""s eye(s). The image is preferably presented at virtual infinity and can be imaged over the peripheral retina (outside the central 10 degrees radius, where patients are typically asymptomatic). A patient is directed to centrally fixate on the random noise display. A visual aid, such as a cross hair, may be included in the generated display to facilitate this focus. With a scanning laser virtual reality device having a narrow exit pupil, the failure of a patient to centrally fixate causes the image presented to be distorted, incomplete or disappear from view. While a patient views the random noise display, the patient is directed to indicate any areas of disturbance using an input device.
A preferred input device is a computer pen and tablet. This is easy to use while also viewing the random noise display. Preferably, the display changes when a patient uses the pen and tablet such that the patient sees the location being indicated either in place of or superimposed upon the random noise display.